The easiest way would probably be to clone the CoH2 bunker (it's called base_defense or something like that in the editor) and replace the path in entity_blueprint_ext with that of the CoH1 bunker. Even the upgrades should work with some minor modifications.
I have a working version of it in a mod that I'm making, but I'm not at home right now. If you need more specific instructions, I can give them later!
Thanks for the quick reply, I'll give it a try this way and let you know if it worked fine for me
or if I need specific advise. Till soon Paladin_SA